Heat transfer system and method



Jan. 26, 1932. F. B. HQNT 1,843,026

HEAT TRANSFER SYSTEM AND METHOD Filed July 17, 1930 2 Sheets-Sheet l f;5 &

i N INVENTOR.

flan/Ell 16.155005 H aa A TTORNE Y.

Jan. 26, 1932. F. B. HUNT Y mm TRANSFER SYSTEM AND METHOD '2Sheets-Sheet 2 Filed July 17, 1930.

#fii 4435/ 1/);71/1 J/ 10/ 1 /71 1/ .2 1/7 1/1 a J j/ /z/ INV ENTORflan/E'khfl/Yanf BY 4WCLM ATTORNEY Patented Jan. 26, 1932 i UNITEDSTATES PATENT OFFICE FRANKLIN B. HUNT, or omcaeo, ILLINOIS, ASSIGNOR'1'0 DRYICE EQUIPMENT conronA'rIon, 01 NEW YORK, N; Y., A. CORPORATIONor DELAWARE HEAT TRANSFER srs'rm AND mmnon Application filed lTuly 17,

My present invention is shown as embodied 1n systems primarily devisedfor transfer of heat from a region or'space to-be niaintamed at adesired refrigerant temperature to a re-.

: frigerant source, and includes means whereby a very intense, that isto say, low temperature refrigerant may be used for refrigeration at a-much higher temperature, the preferred refrigerant'being solidifiedcarbon dioxide in a various forms, compounds and mixtures, no-

tably approximately pure carbon dioxide, at approximately 110 below zeroF. However, various features of. the invention are applicable tovariouslower temperature refrigsubstantially below the boiling point ofthe heat transfer medium.

The heat transfer medium will be selected as preferred. In general, ahigher boiling point medium may be employed where the desiredrefrigerating temperature is relatively high or the heat leaks to berefrigerated 1 againstare relatively small, but its freezing pointshouldbe below the temperature of the condenser. The specific mediumselected may be any of those known totheart, forinstance, sulphurdioxide (S ,ammonia (NH ,carbon dioxide (CO methyl chloride (CH) 501,propane (C l-I etc." i

The systems shown herein include control of temperature of therefrigerated space by having the heat absorbing-coil or evaporator partof the circuit flooded, not flooded, or partly flooded, either (0,) bylocatingsaid evaporator in gravity flow relation to thecondenser andemploying a thermostatically operated .v'alve between the coil and thecondenser to control, permit or prevent flow-of the-condenserliquid fromsaid condenser into said eya'po'rating coil; or (b) to effect the samecontrol of gravity flow by-moving 1930. Serial No. 468,601.

vapor coil above or below the level 0 the liquid ilrtlie-condenser; orby locating the coil at or above the level of the condenser andproviding, a lift line in the form of a small capacity boiler exposedtothe heat of the refrigerated space in such relation that part of theliquid in said lift coil will be evaporated, the incipient bubbling thusproduced serving to decrease the specific gravity the of the liquid inthe lift line so that it is unbalanced and forced upward by the coldliquid in the condenser and, when the boiling becomes pronounced, thebubbles of vapor will exercise a pronounced air lift effect so that whenproportioned and designed to suit the conditions, the main evaporatorwill be properly charged or flooded with liquid. This will occur whentemperatures in the refrigerated-space are too high. Consequently, suchliquid flooded into the evaporator will rapidly absorb heat from therefrigerated space, and the resultant boiling of the liquid willmaintain the evaporator at constant or controlled temperature accordingto the internal pressure on the system.

In order to effect further control, said pressure within the system maybe prede termined and automatically adjusted by v means of a pressurevalve in the llne between the evaporator and the condenser whereby whenthe internal pressure becomes too low by reason of fall of temperaturein the refrigerated space, the return flow of vapor to the condenserwill be blocked.

My invention also includes a specific improved arrangement of condenserwith referen'ceto solid carbon dioxide as the refrigerant, whereby therate of heat transfer to the condenser is reduced so that other things.beingequal the temperature of the condenser itself may be substantiallyhigher than that of the solid carbon dioxide refrigerant. This may be ofadvantage with any .of the above mentioned heat transfer liquids since'has been condensed, is unnecessary.

I operativeness of my apparatus depends mainly on the heat absorbed bythe boiling -modifications Fig. 8 is a detail view of condensercontained in Fig. 1.

In Fig. 1 the refrigerated space 1 is shown as enclosed by heatinsulating casing which may comprise exterior and interior gas-tightshells 2 with intervening heat insulating ma:

terial 3 enclosing,preferably at a high level therein, a refrigerantcontainer 4 WhlCh may be charged with refrigerant such as solidcarbondioxide 5 by removing the hatch 6.

The insulation' i may be very heavy so that only a negligible amount ofheat can be absorbed throu h the walls thereof, directly from the rerigerated space, but it is only necessary that this insulation besufficient so that the refrigerant'efi'ect thus directly exerted uponthe refrigerated space 1 will be at all times insufiicient to keep thetemperature of the refrigerating space 1 down to the desired maximum.That'is to say, so long as such direct refrigeration is insufficient,the control of the exact desired temperature will reside in my heattransfer system which I will now describe.

The heat transfer circuit comprises a condenser 7, fromthe bottom ofwhich the condensed liquid flows through pipe 8 into the refrigeratedspace, thence upward through an accelerating heat absorbing coil 9 andthrough pipe 10 into the top of a boiler 11.

The liquid gravitates to the bottom of this boiler and the vaportherefrom escapes through pipe 12, control valve 13 and pipe 14 back tothe condenser 7. While the liquid may be any known or desired liquidsuch as those above mentioned, we may assume for present purposes thatsulphur dioxide (S0 is used. The amount of liquid charged into thesystem should 'be such that even when I the amount of liquid containedin the condenser 7 and coil 9 is a maximum, there will still be someliquid left in the bottom of the evaporator 11.

The liquid in evaporator 11 is exposed to the atmosphere in therefrigerated space 1 and, absorbing heat from the latter, will evaporatesufiiciently to generate a pressure in the system corresponding to thesaturation pressure of sulphur dioxide for .that temperature. The vaporin the condenser -7 will of course be at the same pressure as in 11,:

but being in contact with the cold surfaces of the condenser .7condense, thereby 'phur dioxide will boil at the same rate that thecondenser 7 can condense it. The boiling off of the liquid removes someof the heat from the evaporator 11 and lowers the temperature in therefrigerated space 1. The coil and condenser will now come to equilib-'rium for this lower temperature in space 1; the temperature of theevaporator will drop and correspondingly the pressure in the entiresystem will drop. 1

It is thus evident that the functioning oi the system is governed inaccordance with its internal pressure and an important feature oi theparticular system shown in thisFig. 1 is providing the valve 13 betweenthe evaporator 11 and condenser 7, which may be used to control thispressure, preferably automatically. When the valve is open, the abovedescribed cycle of boiling in the evaporator 11 and condensing in thecondenser 7 continues unmodified, but if the valve be closed, the vaporescaping from the evaporator cannot flow through its normal path to thecondenser and the pressure automatically rises. the result being thatthe boiling point of the liquid in the system is raised above thetemperature of evaporator 11. Ofcourse, the rise of pressure takeseffect as a back pressure through coil 9, but this has no other eifecithan to force part of the liquid in that coil back into the condenser.Boiling being thus prevented, the rate of heat absorption in coil 11 isgreatly decreased, thereby permitting the temperature in spacel to rise.While such a valve could be operated by hand 01 thermostatically, thepresent preferred arrangement is one in which the valve automaticallyopens upon rise of pressure, therebypermitting vapor again to flow intothe condenser an closes on fall of pressure cuttin off such flow. Themeans diagrammatical y indicated for this purpose is a metallic bellows15, the exterior of which is exposed to atmospheric pressure throughvent 16, and the interior of 'which is exposed to the interior pressureof the system through inlet 17. The normal position of the valve iscontrolled by balance between an interior spring 18 and exterior spring19 and may be set to operate at desired internal pressures by anadjusting screw 20, whereby the exterior spring 19 may be 31-: undergreater or less nitial pressure ten g toclose. the valve'13. It will benoted. that the inlet to theev'aporator 11 is at a point above thenormal level ofli'quid in the system and no liquid would normall flow bygravity from the condenser mosphere in the refrigerated space 1, but itI may be arranged in the walls the refrigerator or partly or whollyoutside the same.

The heat operates first to decrease the specific gravity of the liquidin this coil, up to the boiling point thereof; and thereafter will causeincipient bubbling and ultimately boiling of the liquid in said coil towhatever extent .may be necessary to decrease the specific gravity ofthe liquid to a point where the cold, heavy liquid remaining in thecondenser will overbalance the light liquid in 9. and force some of themixture to flow'into the evaporator 11.

It will be noted that in thus functioning, the lift coil 9 isthermostatic in so much as the warmer it gets, the more effectiveit-will be in lifting liquid and supplying it to the evaporator.

A special feature of the system shown in Fig. l is the peculiar form ofcondenser and means for conducting heat therefrom into intimate and sureheat exchange relation with the solid carbon dioxide. In the form shownin Fig. 1, and more in detail in Fig. 8, the condenser consists of twoplates, 27, 28,

held parallel by spacer framing strip 29 affording a con enserinterspace 30 which is rendered gas-proof under. any pressure that maybe exerted in the system by welding the plates to the spacer. As shownin Fig. 8, the spacer is preferably formed with an inclined bottom sothat all liquid may be drained therefrom through pipe 8. The rear plate,28, of the condenser is integral with a horizontal plate 28a extendinglaterally over the bottom of the bunker, so that the solid carbondioxide 5 rests on said plate.

:- With such an arrangement, the heat from the condenser reaches thesolid carbon dioxide mainly by conduction through the all metal pathaiforded by 28a, and the amount of heat absorbed depends on the area ofcontact. of the refrigerant block 5 with said plate.

Consequently, said block 5 may be 'evapo-' rated down tov a thin slabbefore there is any -substantial decrease in the refrigerating effectwhich it exerts on the condenser. The

heat conveyed from the condenser to the refrigerant may be stillfurtherlimited to that which flows through the all metal path by"ap-' plying alayer 31 of compressed cork or other heat insulating material over theface of condenser plate 30, between it and the refrigerant 5.

'Ihe carbon dioxide gas evolved incontainer 4 maintains the latter fullof pure cold which has a remarkable insulating effect 5:?! furtherlimits leak of heat to the solid responding to drop below the desiredtemperature.

"if desired, or ma be returned to the bunker.

Other-modifie systems in accordance with my present invention areillustrated in Figs. 2 to 7 inclusive. In these figures, parts corig. 1are represented by the same reference 11 merals, distinction betweenfigures being'pr served by the use of dif ferent exponen for thenumerals of each figure.

In Fig. 2, the space laxis to be cooled to, and maintained at, somedefinite temperature considerably higher than the temperature of thesource of refrigeration which is con tainedin 4a and which may be verycold brine, solid carbon dioxide, liquid air or the lik For a specificcase, one may assume that the refrigerant is solid carbon dioxide whichevaporates at 'a temperature of 11 0 F. and that space 1a is to becooled to a temperature of 40 F.

The condenser 7 a is indicated as a coil in refrigerant compartment 4aso that if vapor of some volatile liquid is introduced therein, itslatent heat will be removed, thereby condensing it to liquid. Thiscondenseris connected by pipe 8a with the evaporator 11a which is in therefrigerated space 1a and is at a lower level so that liquid from thecondenser 7 a will drain by gravity into the top of said evaporator andthe lower end ofthe latter is connected by pipe 12a with the top ofcondenser 7a. Drainage of liquid is controlled from the condenser intothe evaporator by 'a valve 13a, which isdiagrammatlcally indicated ascontrolled by a thermostatic above the desired temperature and to closesaid valve when the temperature tends to In operationwe may assume thatthe condenser 7 a is filled with sulphur dioxide; thati bunker 4acontains solid carbon dioxide; and that space 1a is at a temperature of70. Since the bulb F is adjusted to open valve 13a at40, a

liquid in 7a is free to flow into coil 11a. The warm atmosphere around11a vaporizesthe liquid and the vapor flows through ipe 12a to thecondenser .7 a where its heat 0 vaporization is removed and it becomesliquid. This liquid drains into coil 11a, where'it is again vapprized,thereby removing more heat from space 1a. This cycle continues until thedesired temperature (40 F.) is reached in space 1a, whereupon thethermostatic bulb closes valve 13a, so that liquid sulphur dioxide canno longer flow from 7a to 11a and refrigerating of space 1a is arrested.As soon as the temperature starts to rise, the bulb again opens valve13a and the cycle of the sulphur dioxide through the system is resumedand continues until the temperature is again, lowered to the point wherethe bulb F will again close the valve 130. Thus, as long as there isrefrigerant in bunker 4a sufficient to condense the sulphur dioxidevapor, space 10 will be maintained at F. although the temperature of therefrigerant is about 110 F. Similarly, the valve 130: can 'be adjustedfor other temperatures such as and flow to condenser 7a, thus preventingany rise of pressure such as operates to discon tinue the boiling inFig. 1 where the valve is between the evaporator and the condenser. Thecontrol valve is, and in all systems may be, the well known type ofsnap-action valve now employed in mechanical refrigeratorsthe'characteristic ofwhich is that it remains wide open until apredetermined low pressure is reached and, having reached this lowpres-- sure and having closed, it remains closed until a predeterminedhigh pressure is reached.

In Fig. 2, .the evaporator 11a has to be at a low level in order toinsure gravity drainage of liquid into it from the condenser 7a and thisis frequentlyundesirable because the bottom of the refrigeratornaturally tendsto be the coldest part thereof and unless the heat isabsorbed in the upper warmer part of the atmosphere, the convectioncurrents will not be sufficient tomaintain reasonable uniformity oftemperature between the top and the bottom of said space. However, thesystem shown in Fig. 2 may be made to operate with the coil in the upperpart. of the re-. frigerated space by providing an air lift pipe 96,which operates on the principle described in connection with the coil 9of Fig. 1, that is to say, if the system is filled with liquid to theliquid through the distance a; plus 3 when-' height indicated by thedotted llne w, the part of it in9b being exposed to the heat in theupper part of the refrigerated space 1?), will cause incipient boilingsuflicient to lift ever the thermostatic valve 136 is open, Ob-

' viously, said, valve 131) can be located in the return conduit 126 ifdesired, in which case M vapor formed in 116 after the'valve is closedwill be cut oil from condenser 7 b and can only take effect as backpressure raising the level of the liquid in the condenser 7 1).Obviously, such a-valve can be located anywhere in the exterior part ofthe circuit in or between the .condenser outlet 86 and the condenserinlet 12b. e I I I The evaporator coil may be modified'in several wayswithout changing the basic principle of operation. I In Fig. 4,- coil110 is supposed to be the same as coil 11b of Fig. 3, but it is providedwith short circuiting pipes 1110, 11m, to afford short paths for vaporreturn from different parts of the coil so that the vapor will not tendto lift the liquid back towards its source. I

In Fig. 5, I have shown means whereby the liquid-may be raised to anevaporator coil lid, located at any desired height. This is accomplishedby one or anydesired number of loops 11y, 112, connected in parallel tothe low level drainage pipe 8d of condenser 7d and re-entering theraiser pipe 9d at asub- I stantially higher level.- In this waya desiredamount of the cold liquid, may be heated enough to lift it to therequired height. The

heat and the absorbing capacity of these loopsmay be such-as to causepracticall all of the frosting to occur onsaidloops, l eaving theevaporator coil 11d, free from frost 'or alternately frosted anddefrosted, in cases where the refrigerant temperature in 1d is at orabove the freezing point of water.

If it is necessary or desirable to elevate the evaporator 11d, to alevel as high or high- ;er than that shown in Fig. 5, additional liftingeffect for the liquid in 9a may be obtained by using as many loops, withas much heat absorbing surface as may be necessary to give proper airlift? for the liquid, in any particular case. If a thermostatic valve isused, it can be placed'either in evaporator coil 11d or in the loopsthemselves.

In Fig. 6, I have shown how two differentcompartments, 1m, 1 can berefrigerated at different temperatures by separate evaporators 11c and11 connected in parallel with the same refrigerant condenser 7e. Whileany'ofthe herein described systems can be thus connected to a singlesource, by the use of lifting-loops or coils where these are necessary,the specific form here shown is Where one of the evaporators 'isbelowthelevel of the condenser and in this case-the condensed liquid in 86passes through branch pipes 8f and 9;, each' provided with an outwardlyopening check valve 8g, 9g, while the vapor returns areconnected with 12by pipe 12/,

12a, respectively. 129 will contain a stand:

ard control valve 13, which may be of the type shown in F ig. 1, while12f will be controlled by snap action control valve 13!; such asdescribed in connection with Fig. 2.

Thus, there aretwo heat absorbing systems operating independently-fromthe same condenser 70. When the compartment-1y reaches a desiredtemperature, say10,- valve 13 will operate to discontinue evaporationinevaporator 11c. Likewise when 11f pm.

. being indicated in Fig. 7 where the condenser 7a has'a reservoir 7 oto assist in determining liquid in the system will be normally;

The above noted tendency of the lift line to respond thermostatically tothe temperature in the refrigerated space may be utilized as the solethermostatic control factor of the system, one arrangement for suchpurpose a definite normal level for liquid in the condenser while theevaporator lln is,- located wholly above said level so as normally tocontain no liquid. In this case the drainage pipe 8% drains directlyinto a loop 110, which exposes enough heat absorbing area in therefrigerated space 1n so that the liquid is warmed above the frostingpoint by the time it reaches the lift coil 9n. Normally, the cold liquidflows to the bottom leg of the coil 110 and as it becomes heatedrisesinto the lift coil 91, the shunt pipe 80 having little or no effecton'this natural thermocirculation' of the liquid. However, whenbubblingand upflow of liquid becomes copious, 80 may come into action tosupply liquid directly to the lift coil, 9%. The coil 110' may have suchheat absorbing capacity as vto warm the liq uid above the frost point,when the refrigerant temperature in In 'is substantially above.

32 -F., otherwise there may be frost on lift coil 9n, but thefunctioning will be upon the same principle as where there is no frostformation. That is to say, the main evapomtor lln, being above thenormal level of the dry and they only boiling that occurs will e in theloop 110 and lift coil 9n. Whenever this becomes excessive, however, theliquid will progressively invade the evaporator lln and the heatabsorption and transfer will be increased accordingly.

Iclaim:

1. A method of refrigeration which includes evaporating a liquid by heatabsorbed in a region to be cooled; conducting resulting vapor inoperative relation to the refrigerant,

, to recondense the same to liquid, said recondensation taking place in.one portion of a condenser while the heat is conducted to therefrigerant in a different portion of the com denser through acomparatively thick metallic path; conductingthe liquid back to theregion to be cooled in continuous circuit; and

controlling evaporation to control the temperature in therefrigeratedregion by controlling fiow of fluid between the evaporator and thecondenser.

2. A- method of refrigeration which includes evaporating a liquid byheat'absorbed in a region to be cooled; conducting resultingvapor inoperative relation to the refrigerant, to recondense the same to liquid,said recondensation taking place in one portion of'a condenser while theheat is conducted to therefrigerant in a diflferent portion of thecondenser through a comparatively thick metallic path conducting theliquid back to the in a region to be cooled; conducting resulting vaporin operative relation to the refrigerant; to recondense the same toliquid, sa1d recondensation taking place in one portion of a-condenserwhile the heat is conducted to the refrigerant in a different portion ofthe condenser through a comparatively thick metallic path; conductingthe liquid back to the region to' be cooled in continuous circuit; and

controlling evaporation to control the temperature in the refrigeratedregion by causing decrease of pressure in the system to cut off returnof the vapor to the condenser.

4. A method of refri eration which includes evaporating a liquid by heatabsorbed in a region to be cooled; conducting resulting vapor inoperative relation to the refrigerant, to recondense the same to liquid,said recondensation taking place'in' one orti'on of a condenser whilethe heat is 0011 noted. to the refrigerant in a different portion of thecondenser through a comparatively thick metallic path; conducting theliquid back to the region to be cooled in continuous circuit; and

ing changes of pressure in the system due to changes of temperature inthe refrigerated space to control return flow of the vapor to thecondenser, I

5. A method of refrigeration which include's evaporating a liquid byheat absorbed in a region to be cooled conducting resulting vapor inoperative relation to the refrigerant, to recondense the same to liquid,saidrecondensation taking place in one ortion of a condenser while theheat is con noted to the refrigerant in a different portion of thecondenser through a comparatively thick metallic path; conducting theliquid back to the region to be cooled in continuous circuit; andcontrolling evaporation to control the temperature in the refrigeratedregion by utilizingchanges of pressure in the system due to changes oftemperature in the refrigerated [space to cut off flow of the vapor tothe coning vapor in operative relation to the refrigerant, to recondensethe same to liquid;

conducting the liquid back to the region tobe cooled in continuouscircuit; and controlling evaporation to control the temperature in therefrigerated region by locating the inlet to the vaporative portion ofthe circuit at a level higher than the normal level of condensed liquidin the circuit and utilizing heat ab-- sorbed from the refrigeratedspace by the liquid in its path from condenser to the evap orator towarm and partially vaporize the liquid to lift it above said normallevel a distance sufficient to cause the liquid to'over- 4 densed liquidin the circuit and utilizing heat absorbed from the refrigerated spaceby the liquid in its path from condenser to the evaporator to warm andpartially vaporize the liquid to lift it above said normal level adistance suflicient to cause the liquid .to overflow into the evaporatoror to not overflow,

according as the amount of heat so absorbed is greater or less.

8. The method of modifying the refrigerative effect of solid carbondioxide on a condenser that has a condenser portion and a plateextending therefrom which includes conducting the heat from thecondenser through an all-metal path including said metal plate and uponwhich the solid carbon dioxide is supported.

9. A closed circuit refrigerating system including an evaporator forboiling a liquid by heat absorbed in a region to be cooled; a

conduit conducting resulting vapor to a condenser in operative relationto a refrigerant, thereby recondensing the same to liquid, sa idrecondensation taking place in one portion of the condenser while theheating is conducted to the refrigerant in a different portion of thecondenser through a comparatively thick inetallic path; a return conduitfor conduct ing the liquid back to the region to be cooled,

in continuous circuit; and means for controlling the temperature whichincludes valve means for controlling, permitting or preventing flow offiuid in said circuit.

it A'closed circuit refrigerating system including an evaporator forboiling a liquid by heat absorbed in a region to be cooled; a

conduit conducting resulting vapor to a con-'v denser in operativerelation to a refrigerant,

recondensation taking place'in one portion thereby recondensing the sameto liquid, said" i of the condenser while the heating is conducted tothe refrigerant in a different portion of the condenser through acomparatively thickmetallic path; a return conduit for conducting theliquid back to the region to be cooled, in continuous circuit; and meansfor controlling the. temperature which includes valve means forpreventing return fiowof the vapor to the condensenf 11. A closedcircuit refrigerating system by heat absorbed in a region to be cooled;a conduit conducting resulting vapor to a condenser in operativerelation to a refrigerant,

thereby recondensing the same to liquid, said recondensation takingplace in one portion of the condenser while the heating is conductedto-the refrigerant in a different portion of the condenser through acomparatively thick metallic path; a return conduit for conducting theliquid back to theregion to be cooled, in continuous circuit; and meansfor controlling the tcmperature which includes automatic valve meansutilizing decrease of pressure in the system to cut off return of thevapor to the condenser.

12. A closed circuit refriger ting system including an evaporator forboi ing a liquid by heat absorbed in aregion to be cooled; a conduitconducting resulting vapor to a condenser in operative. relation to arefrigerant, thereby recondensing the same to liquid, saidrecondensatio'n taking place in one portionof the condenser while theheating is conducted to the refrigerant in a different portion of thecondenser through a comparatively thick metallic Path; a return conduitfor conducting the liquid back to the region to be cooled, in continuouscircuit; and

means for controlling the temperature which includes automatic valvemeans utilizing changes of pressure in the systemv due to changes of.temperature in the refrigerated space to control return flow of thevapor to the condenser.

13. A closed circuit refrigerating system including an evaporator forboiling a liquid by heat absorbed in a region to be cooled; a conduitconducting resulting vapor to a condenser in operative relation to arefrigerant, thereby recondensing the same to liquid, saidrecondensation taking place in one portion of the condenser while theheating is conducted to the refrigerant in a different portion of thecondenser through a comparatively thick netallic path; a return conduitfor conducting the liquid back to the region to-be cooled, in continuouscircuit; and means for controlling the temperature which includesautomatic valve means operating to cut off new of the vapor to :thecondenser'when the temperature falls below. predetermined minimum andtopermit flow to the condenser when the temperature rises above apredetermined maximum.

.14. 'A closed circuit refrigerating system including an evaporator forboiling a liquid including an evaporator for boiling a liquid i by heatabsorbed in a region to be cooled; a

conduit conducting resulting vapor to .a condenser in operative relationto a refrigerant,

thereby recondensing the same toliquid; a return conduit for conductingthe liquid back to the reglon to be cooled, 1n continuous c rcuit, theinlet-to the-evaporator being at a level higher than the normallevelof'condensed liquid in the system and the liquid,

including an evaporator for boiling a liquid by heat absorbed in aregion to'becooled; a-

conduit conducting resulting vapor to a condenser in operative relationto a refrigerant, thereby recondensing the'same to liquid; areturnconduit for conducting the liquid back to the region to be cooled,incontinuous circuit, the inlet to the evaporator being at a levelhigher than the normallevel of condensed liquid in the system and theliquid supply conduit tothe evaporator being de- Signed and located toabsorb heat-from the refrigerated space to Warm and partially vaporizethe liquid to lift it above said normal level a distance sufficient tocause the liquid to overflow into the evaporator ornot to overflow,according as the amount of heat so absorbed is greater orless.

"- 16. Refrigerating apparatus, including a closed circuit through acondenser in heat transfer relation to a refrigerated. source, adischarge conduitfor liquid therefrom. an evaporator in the refrigeratedspace into wh ch said conduitdischarges, a return conduit for vapor fromthe evaporator to the condenser, the inlet of the evaporator being, at alevel above the normal level of liquid in a the condenser and the liquiddischarge conduit from the condenser to the evaporator having in shuntthereon an auxiliary conduit exposed to heat from or varying with thetemperature of refrigerated space and of heat absorbing capacitysuflicient to cause partial boiling of liquid therein to lift the liquidin said discharge conduit above the level oftl e liquid in thecondenserand discharge it into the evaporator.

17. Refrigerating apparatus, including a closed circuit through acondenser in heat transfer relation to a refri erant source, a dischargeconduit for liquid therefrom, an evaporator in the refrigerated spaceinto which said conduitdischarges, areturn conduit for vapor from theevaporator to the condenser, designed and operating to maintain abovefreezing temperatures in the refrigerated space, the liquid dischargeconduit from the condenser exposed to heat from the atmosphere of thespace to be refrigerated and of heat absorbing capacity sufiicienttoWarm the liquid above frostcollecting temperature before it enters theevaporator.

18.,Refrigerating apparatus, including a' closed circuit through acondenser in heat transfer relation'to a refrigerantsource, a dischargeconduit for liquid therefrom. an evaporator in the refrigerated spaceinto which said conduit diseharges,-'a return couduit for vapor from theevaporatorto the condenser, said latter conduit having a low level loopexposed to the atmosphere of the space to berefrigerated and of heatabsorbing capacity sufficient vtoflsubstantially warm the liquid beforeit enters the evaporator.

19, Refrigerating apparatus, including an outer heat-insulating casingprovided with an inner g'as-tight shell forming an interspace forcirculation of carbon dioxide gas between it and the outer casing; a"container for solid carbon dioxide in the upperportion of saidchamber,arranged for overflow of gas therefrom into said interspace and providedwith v heavy heat insulation between it and the chamber to berefrigerated, thereby minimizing 'dlrect heat transfer; ametali'condenser therein having its'inlet' at a relatively high leveland its outlet at a-lower level and having a transverse integralextension upon which SOllCllfiBd carbon dioxide refrigerant issupported, thereby affording an all metal pathfortransfer ofheat fromthe condenser't'othe refrigerant; a-"discharge conduit from the lowerportion of the condenser extending into the refrigerated space, anevaporator in the refrigerated spaceinto which said conduit discharges,a return conduit closing aclosed circuit return for vapor fromtheevaporator to the condenser, ,and means for controllingthe rate ofevaporation in the evaporator by and in accordance with the temperatureof the refrigerated chamber.

20. Refrigerating apparatus, including an .outer heat-insulating casingprovided with an inner gas-tight shell-forming an interspace forcirculation of carbon" dioxide gas between it and the outer casing; acontainer for 'solid carbon dioxide in'the upper portion of saidchamber,'arranged for joverfiow of.

gas therefrom into said interspace and pro-' vided with heavy heatinsulation between it and the chamber to be refrigerated, therebyminimizing direct heat trans fer; a metal 011-.

denser therein having its inlet at a relatively higlrlevel and its,outlet at'a lower level and having a transverse integral extensionuponvvhich solidified carbon dioxide refrigerant is supported, therebyaffording an all metal path for transfer of heat from the condenser tothe refrigerant and heat insulating ma terial interposed laterallybetween the solid carbon dioxide and the condenser to minimize direct.transfer of heat; a discharge conduit from the lower portion of thecondenser ex;

' tending into the refrigerated space, an evaporator in the refrigeratedspace intowhich said conduit discharges, a return conduit closing aclosed circuit return for vapor from the evaporator to the condenser,and means for controlling the rate of evaporation in the evaporatorby'and-in accordance with the temperature of the refrigerated chamber.

21. Refrigerating apparatus, including an insulating casing, a containerfor solid carbon dioxide provided with heavy heat insulation, therebyminimizing direct heat transfer to the exterior, a metal heat exchangedevice for circulation of a fluid to be cooled which includes acondenser portion and a transverse metal plate extending therefrom andbeing within said container upon which the solidifiedcarbon dioxiderefrigerant is supported, thereby affording an all metal path fortransfer of heat from the heat exchange device to refrigerant torecondense the same to liquid,-

said recondensation taking place in one portion of a condenser while theheat is conducted to the refrigerant in a dilferent portion of thecondenser through a comparatively thick metallic path, conducting theliquid back to the regions tobe cooled in separate circuits, andcontrolling evaporation to control the temperatures in the refrigeratedregions by controlling flow of fluid between the 'evap'orators and thecondenser.

23. method of refrigeration which in.- cludes evaporating a liquid byheat absorbed in a region to be cooled, conducting resulting vapor inoperative relation-to the refrigerarranged so that the solid carbondioxide is in heat conducting relationship therewith whereby heat isabsorbed mainly by conduction through said solid portion.

' 25, An apparatus for refrigerating with solid carbon dioxide whichcomprises an outer container, 2, solid carbon dioxide chamber withinsaid container, a fluid condenser having a hollow portion for condensingthe fluid and a fluid inlet and outlet communication with said hollowportion and a solid portion extending therefrom, said solid-portionbeing arranged to support the solid carbon dioxide, whereby heat isabsorbed mainly by conduction through said solid portion.

' Signed at Chicago, in the county of Cook, and State of Illinois, this23rd day of June,

FRANKLIN B. HUNT.

ant, to recondense the same to liquid, said recondensation taking placein one portion of a condenser while the heat is conducted to therefrigerant in a different portion of the condenser through acomparatively thick me tallic path, conducting the liquid back to theregion to be cooled in continuous circuit, controlling evaporation tocontrol the temperatures in the refrigerated region by preventing returnflow-of the vapor to the condenser;

and maintaining the rate of condensation substantially uniform byinterposlng suitable insulationv between said condensing portion and therefrigerant, thus preventing substantially all direct heat absorptiontherebetween. 24. An apparatus for refrigerating with solid carbondioxide which comprises an outer container, a solid carbon dioxidechamber within said container, a fluid condenser having a hollowport-ion for condensing the fluidand a fluid inlet and outletcommunication with said hollow portion and a solid portion extendingtherefrom, said solid portion being

